/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1991, 1993
 *  The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *  @(#)queue.h 8.5 (Berkeley) 8/20/94
 * $FreeBSD$
 */

#ifndef _SYS_QUEUE_H_
#define _SYS_QUEUE_H_

/*
 * This file defines four types of data structures: singly-linked lists,
 * singly-linked tail queues, lists and tail queues.
 *
 * A singly-linked list is headed by a single forward pointer. The elements
 * are singly linked for minimum space and pointer manipulation overhead at
 * the expense of O(n) removal for arbitrary elements. New elements can be
 * added to the list after an existing element or at the head of the list.
 * Elements being removed from the head of the list should use the explicit
 * macro for this purpose for optimum efficiency. A singly-linked list may
 * only be traversed in the forward direction.  Singly-linked lists are ideal
 * for applications with large datasets and few or no removals or for
 * implementing a LIFO queue.
 *
 * A singly-linked tail queue is headed by a pair of pointers, one to the
 * head of the list and the other to the tail of the list. The elements are
 * singly linked for minimum space and pointer manipulation overhead at the
 * expense of O(n) removal for arbitrary elements. New elements can be added
 * to the list after an existing element, at the head of the list, or at the
 * end of the list. Elements being removed from the head of the tail queue
 * should use the explicit macro for this purpose for optimum efficiency.
 * A singly-linked tail queue may only be traversed in the forward direction.
 * Singly-linked tail queues are ideal for applications with large datasets
 * and few or no removals or for implementing a FIFO queue.
 *
 * A list is headed by a single forward pointer (or an array of forward
 * pointers for a hash table header). The elements are doubly linked
 * so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before
 * or after an existing element or at the head of the list. A list
 * may be traversed in either direction.
 *
 * A tail queue is headed by a pair of pointers, one to the head of the
 * list and the other to the tail of the list. The elements are doubly
 * linked so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before or
 * after an existing element, at the head of the list, or at the end of
 * the list. A tail queue may be traversed in either direction.
 *
 * For details on the use of these macros, see the queue(3) manual page.
 *
 * Below is a summary of implemented functions where:
 *  +  means the macro is available
 *  -  means the macro is not available
 *  s  means the macro is available but is slow (runs in O(n) time)
 *
 *        SLIST LIST  STAILQ  TAILQ
 * _HEAD      + + + +
 * _CLASS_HEAD      + + + +
 * _HEAD_INITIALIZER    + + + +
 * _ENTRY     + + + +
 * _CLASS_ENTRY     + + + +
 * _INIT      + + + +
 * _EMPTY     + + + +
 * _END       + + + +
 * _FIRST     + + + +
 * _NEXT      + + + +
 * _PREV      - + - +
 * _LAST      - - + +
 * _LAST_FAST     - - - +
 * _FOREACH     + + + +
 * _FOREACH_FROM    + + + +
 * _FOREACH_SAFE    + + + +
 * _FOREACH_FROM_SAFE   + + + +
 * _FOREACH_REVERSE   - - - +
 * _FOREACH_REVERSE_FROM  - - - +
 * _FOREACH_REVERSE_SAFE  - - - +
 * _FOREACH_REVERSE_FROM_SAFE - - - +
 * _INSERT_HEAD     + + + +
 * _INSERT_BEFORE   - + - +
 * _INSERT_AFTER    + + + +
 * _INSERT_TAIL     - - + +
 * _CONCAT      s s + +
 * _REMOVE_AFTER    + - + -
 * _REMOVE_HEAD     + - + -
 * _REMOVE      s + s +
 * _SWAP      + + + +
 *
 */
#ifdef QUEUE_MACRO_DEBUG
#warn Use QUEUE_MACRO_DEBUG_TRACE and/or QUEUE_MACRO_DEBUG_TRASH
#define QUEUE_MACRO_DEBUG_TRACE
#define QUEUE_MACRO_DEBUG_TRASH
#endif

#ifdef QUEUE_MACRO_DEBUG_TRACE
/* Store the last 2 places the queue element or head was altered */
struct qm_trace {
  unsigned long  lastline;
  unsigned long  prevline;
  const char  *lastfile;
  const char  *prevfile;
};

#define TRACEBUF  struct qm_trace trace;
#define TRACEBUF_INITIALIZER  { __LINE__, 0, __FILE__, NULL } ,

#define QMD_TRACE_HEAD(head) do {         \
  (head)->trace.prevline = (head)->trace.lastline;    \
  (head)->trace.prevfile = (head)->trace.lastfile;    \
  (head)->trace.lastline = __LINE__;        \
  (head)->trace.lastfile = __FILE__;        \
} while (0)

#define QMD_TRACE_ELEM(elem) do {         \
  (elem)->trace.prevline = (elem)->trace.lastline;    \
  (elem)->trace.prevfile = (elem)->trace.lastfile;    \
  (elem)->trace.lastline = __LINE__;        \
  (elem)->trace.lastfile = __FILE__;        \
} while (0)

#else /* !QUEUE_MACRO_DEBUG_TRACE */
#define QMD_TRACE_ELEM(elem)
#define QMD_TRACE_HEAD(head)
#define TRACEBUF
#define TRACEBUF_INITIALIZER
#endif  /* QUEUE_MACRO_DEBUG_TRACE */

#ifdef QUEUE_MACRO_DEBUG_TRASH
#define QMD_SAVELINK(name, link)  void **name = (void *)&(link)
#define TRASHIT(x)    do {(x) = (void *)-1;} while (0)
#define QMD_IS_TRASHED(x) ((x) == (void *)(intptr_t)-1)
#else /* !QUEUE_MACRO_DEBUG_TRASH */
#define QMD_SAVELINK(name, link)
#define TRASHIT(x)
#define QMD_IS_TRASHED(x) 0
#endif  /* QUEUE_MACRO_DEBUG_TRASH */

#ifdef __cplusplus
/*
 * In C++ there can be structure lists and class lists:
 */
#define QUEUE_TYPEOF(type) type
#else
#define QUEUE_TYPEOF(type) struct type
#endif

/*
 * Singly-linked List declarations.
 */
#define SLIST_HEAD(name, type)            \
struct name {               \
  struct type *slh_first; /* first element */     \
}

#define SLIST_CLASS_HEAD(name, type)          \
struct name {               \
  class type *slh_first;  /* first element */     \
}

#define SLIST_HEAD_INITIALIZER(head)          \
  { NULL }

#define SLIST_ENTRY(type)           \
struct {                \
  struct type *sle_next;  /* next element */      \
}

#define SLIST_CLASS_ENTRY(type)           \
struct {                \
  class type *sle_next;   /* next element */    \
}

/*
 * Singly-linked List functions.
 */
#if (defined(_KERNEL) && defined(INVARIANTS))
#define QMD_SLIST_CHECK_PREVPTR(prevp, elm) do {      \
  if (*(prevp) != (elm))            \
    panic("Bad prevptr *(%p) == %p != %p",      \
        (prevp), *(prevp), (elm));        \
} while (0)
#else
#define QMD_SLIST_CHECK_PREVPTR(prevp, elm)
#endif

#define SLIST_CONCAT(head1, head2, type, field) do {      \
  QUEUE_TYPEOF(type) *curelm = SLIST_FIRST(head1);    \
  if (curelm == NULL) {           \
    if ((SLIST_FIRST(head1) = SLIST_FIRST(head2)) != NULL)  \
      SLIST_INIT(head2);        \
  } else if (SLIST_FIRST(head2) != NULL) {      \
    while (SLIST_NEXT(curelm, field) != NULL)   \
      curelm = SLIST_NEXT(curelm, field);   \
    SLIST_NEXT(curelm, field) = SLIST_FIRST(head2);   \
    SLIST_INIT(head2);          \
  }               \
} while (0)

#define SLIST_EMPTY(head) ((head)->slh_first == NULL)

#define SLIST_FIRST(head) ((head)->slh_first)

#define SLIST_FOREACH(var, head, field)         \
  for ((var) = SLIST_FIRST((head));       \
      (var);              \
      (var) = SLIST_NEXT((var), field))

#define SLIST_FOREACH_FROM(var, head, field)        \
  for ((var) = ((var) ? (var) : SLIST_FIRST((head)));   \
      (var);              \
      (var) = SLIST_NEXT((var), field))

#define SLIST_FOREACH_SAFE(var, head, field, tvar)      \
  for ((var) = SLIST_FIRST((head));       \
      (var) && ((tvar) = SLIST_NEXT((var), field), 1);    \
      (var) = (tvar))

#define SLIST_FOREACH_FROM_SAFE(var, head, field, tvar)     \
  for ((var) = ((var) ? (var) : SLIST_FIRST((head)));   \
      (var) && ((tvar) = SLIST_NEXT((var), field), 1);    \
      (var) = (tvar))

#define SLIST_FOREACH_PREVPTR(var, varp, head, field)     \
  for ((varp) = &SLIST_FIRST((head));       \
      ((var) = *(varp)) != NULL;          \
      (varp) = &SLIST_NEXT((var), field))

#define SLIST_INIT(head) do {           \
  SLIST_FIRST((head)) = NULL;         \
} while (0)

#define SLIST_INSERT_AFTER(slistelm, elm, field) do {     \
  SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field); \
  SLIST_NEXT((slistelm), field) = (elm);        \
} while (0)

#define SLIST_INSERT_HEAD(head, elm, field) do {      \
  SLIST_NEXT((elm), field) = SLIST_FIRST((head));     \
  SLIST_FIRST((head)) = (elm);          \
} while (0)

#define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)

#define SLIST_REMOVE(head, elm, type, field) do {     \
  if (SLIST_FIRST((head)) == (elm)) {       \
    SLIST_REMOVE_HEAD((head), field);     \
  }               \
  else {                \
    QUEUE_TYPEOF(type) *curelm = SLIST_FIRST(head);   \
    while (SLIST_NEXT(curelm, field) != (elm))    \
      curelm = SLIST_NEXT(curelm, field);   \
    SLIST_REMOVE_AFTER(curelm, field);      \
  }               \
} while (0)

#define SLIST_REMOVE_AFTER(elm, field) do {       \
  QMD_SAVELINK(oldnext, SLIST_NEXT(elm, field)->field.sle_next);  \
  SLIST_NEXT(elm, field) =          \
      SLIST_NEXT(SLIST_NEXT(elm, field), field);      \
  TRASHIT(*oldnext);            \
} while (0)

#define SLIST_REMOVE_HEAD(head, field) do {       \
  QMD_SAVELINK(oldnext, SLIST_FIRST(head)->field.sle_next); \
  SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field); \
  TRASHIT(*oldnext);            \
} while (0)

#define SLIST_REMOVE_PREVPTR(prevp, elm, field) do {      \
  QMD_SLIST_CHECK_PREVPTR(prevp, elm);        \
  *(prevp) = SLIST_NEXT(elm, field);        \
  TRASHIT((elm)->field.sle_next);         \
} while (0)

#define SLIST_SWAP(head1, head2, type) do {       \
  QUEUE_TYPEOF(type) *swap_first = SLIST_FIRST(head1);    \
  SLIST_FIRST(head1) = SLIST_FIRST(head2);      \
  SLIST_FIRST(head2) = swap_first;        \
} while (0)

#define SLIST_END(head)   NULL

/*
 * Singly-linked Tail queue declarations.
 */
#define STAILQ_HEAD(name, type)           \
struct name {               \
  struct type *stqh_first;/* first element */     \
  struct type **stqh_last;/* addr of last next element */   \
}

#define STAILQ_CLASS_HEAD(name, type)         \
struct name {               \
  class type *stqh_first; /* first element */     \
  class type **stqh_last; /* addr of last next element */   \
}

#define STAILQ_HEAD_INITIALIZER(head)         \
  { NULL, &(head).stqh_first }

#define STAILQ_ENTRY(type)            \
struct {                \
  struct type *stqe_next; /* next element */      \
}

#define STAILQ_CLASS_ENTRY(type)          \
struct {                \
  class type *stqe_next;  /* next element */      \
}

/*
 * Singly-linked Tail queue functions.
 */
#define STAILQ_CONCAT(head1, head2) do {        \
  if (!STAILQ_EMPTY((head2))) {         \
    *(head1)->stqh_last = (head2)->stqh_first;    \
    (head1)->stqh_last = (head2)->stqh_last;    \
    STAILQ_INIT((head2));         \
  }               \
} while (0)

#define STAILQ_EMPTY(head)  ((head)->stqh_first == NULL)

#define STAILQ_FIRST(head)  ((head)->stqh_first)

#define STAILQ_FOREACH(var, head, field)        \
  for((var) = STAILQ_FIRST((head));       \
     (var);             \
     (var) = STAILQ_NEXT((var), field))

#define STAILQ_FOREACH_FROM(var, head, field)       \
  for ((var) = ((var) ? (var) : STAILQ_FIRST((head)));    \
     (var);             \
     (var) = STAILQ_NEXT((var), field))

#define STAILQ_FOREACH_SAFE(var, head, field, tvar)     \
  for ((var) = STAILQ_FIRST((head));        \
      (var) && ((tvar) = STAILQ_NEXT((var), field), 1);   \
      (var) = (tvar))

#define STAILQ_FOREACH_FROM_SAFE(var, head, field, tvar)    \
  for ((var) = ((var) ? (var) : STAILQ_FIRST((head)));    \
      (var) && ((tvar) = STAILQ_NEXT((var), field), 1);   \
      (var) = (tvar))

#define STAILQ_INIT(head) do {            \
  STAILQ_FIRST((head)) = NULL;          \
  (head)->stqh_last = &STAILQ_FIRST((head));      \
} while (0)

#define STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {   \
  if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL)\
    (head)->stqh_last = &STAILQ_NEXT((elm), field);   \
  STAILQ_NEXT((tqelm), field) = (elm);        \
} while (0)

#define STAILQ_INSERT_HEAD(head, elm, field) do {     \
  if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL) \
    (head)->stqh_last = &STAILQ_NEXT((elm), field);   \
  STAILQ_FIRST((head)) = (elm);         \
} while (0)

#define STAILQ_INSERT_TAIL(head, elm, field) do {     \
  STAILQ_NEXT((elm), field) = NULL;       \
  *(head)->stqh_last = (elm);         \
  (head)->stqh_last = &STAILQ_NEXT((elm), field);     \
} while (0)

#define STAILQ_LAST(head, type, field)        \
  (STAILQ_EMPTY((head)) ? NULL :        \
      __containerof((head)->stqh_last,      \
      QUEUE_TYPEOF(type), field.stqe_next))

#define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)

#define STAILQ_REMOVE(head, elm, type, field) do {      \
  QMD_SAVELINK(oldnext, (elm)->field.stqe_next);      \
  if (STAILQ_FIRST((head)) == (elm)) {        \
    STAILQ_REMOVE_HEAD((head), field);      \
  }               \
  else {                \
    QUEUE_TYPEOF(type) *curelm = STAILQ_FIRST(head);  \
    while (STAILQ_NEXT(curelm, field) != (elm))   \
      curelm = STAILQ_NEXT(curelm, field);    \
    STAILQ_REMOVE_AFTER(head, curelm, field);   \
  }               \
  TRASHIT(*oldnext);            \
} while (0)

#define STAILQ_REMOVE_AFTER(head, elm, field) do {      \
  if ((STAILQ_NEXT(elm, field) =          \
       STAILQ_NEXT(STAILQ_NEXT(elm, field), field)) == NULL)  \
    (head)->stqh_last = &STAILQ_NEXT((elm), field);   \
} while (0)

#define STAILQ_REMOVE_HEAD(head, field) do {        \
  if ((STAILQ_FIRST((head)) =         \
       STAILQ_NEXT(STAILQ_FIRST((head)), field)) == NULL)   \
    (head)->stqh_last = &STAILQ_FIRST((head));    \
} while (0)

#define STAILQ_SWAP(head1, head2, type) do {        \
  QUEUE_TYPEOF(type) *swap_first = STAILQ_FIRST(head1);   \
  QUEUE_TYPEOF(type) **swap_last = (head1)->stqh_last;    \
  STAILQ_FIRST(head1) = STAILQ_FIRST(head2);      \
  (head1)->stqh_last = (head2)->stqh_last;      \
  STAILQ_FIRST(head2) = swap_first;       \
  (head2)->stqh_last = swap_last;         \
  if (STAILQ_EMPTY(head1))          \
    (head1)->stqh_last = &STAILQ_FIRST(head1);    \
  if (STAILQ_EMPTY(head2))          \
    (head2)->stqh_last = &STAILQ_FIRST(head2);    \
} while (0)

#define STAILQ_END(head)  NULL


/*
 * List declarations.
 */
#define LIST_HEAD(name, type)           \
struct name {               \
  struct type *lh_first;  /* first element */     \
}

#define LIST_CLASS_HEAD(name, type)         \
struct name {               \
  class type *lh_first; /* first element */     \
}

#define LIST_HEAD_INITIALIZER(head)         \
  { NULL }

#define LIST_ENTRY(type)            \
struct {                \
  struct type *le_next; /* next element */      \
  struct type **le_prev;  /* address of previous next element */  \
}

#define LIST_CLASS_ENTRY(type)            \
struct {                \
  class type *le_next;  /* next element */      \
  class type **le_prev; /* address of previous next element */  \
}

/*
 * List functions.
 */

#if (defined(_KERNEL) && defined(INVARIANTS))
/*
 * QMD_LIST_CHECK_HEAD(LIST_HEAD *head, LIST_ENTRY NAME)
 *
 * If the list is non-empty, validates that the first element of the list
 * points back at 'head.'
 */
#define QMD_LIST_CHECK_HEAD(head, field) do {       \
  if (LIST_FIRST((head)) != NULL &&       \
      LIST_FIRST((head))->field.le_prev !=      \
       &LIST_FIRST((head)))         \
    panic("Bad list head %p first->prev != head", (head));  \
} while (0)

/*
 * QMD_LIST_CHECK_NEXT(TYPE *elm, LIST_ENTRY NAME)
 *
 * If an element follows 'elm' in the list, validates that the next element
 * points back at 'elm.'
 */
#define QMD_LIST_CHECK_NEXT(elm, field) do {        \
  if (LIST_NEXT((elm), field) != NULL &&        \
      LIST_NEXT((elm), field)->field.le_prev !=     \
       &((elm)->field.le_next))         \
        panic("Bad link elm %p next->prev != elm", (elm));  \
} while (0)

/*
 * QMD_LIST_CHECK_PREV(TYPE *elm, LIST_ENTRY NAME)
 *
 * Validates that the previous element (or head of the list) points to 'elm.'
 */
#define QMD_LIST_CHECK_PREV(elm, field) do {        \
  if (*(elm)->field.le_prev != (elm))       \
    panic("Bad link elm %p prev->next != elm", (elm));  \
} while (0)
#else
#define QMD_LIST_CHECK_HEAD(head, field)
#define QMD_LIST_CHECK_NEXT(elm, field)
#define QMD_LIST_CHECK_PREV(elm, field)
#endif /* (_KERNEL && INVARIANTS) */

#define LIST_CONCAT(head1, head2, type, field) do {           \
  QUEUE_TYPEOF(type) *curelm = LIST_FIRST(head1);           \
  if (curelm == NULL) {                 \
    if ((LIST_FIRST(head1) = LIST_FIRST(head2)) != NULL) {        \
      LIST_FIRST(head2)->field.le_prev =          \
          &LIST_FIRST((head1));           \
      LIST_INIT(head2);             \
    }                   \
  } else if (LIST_FIRST(head2) != NULL) {             \
    while (LIST_NEXT(curelm, field) != NULL)          \
      curelm = LIST_NEXT(curelm, field);          \
    LIST_NEXT(curelm, field) = LIST_FIRST(head2);         \
    LIST_FIRST(head2)->field.le_prev = &LIST_NEXT(curelm, field); \
    LIST_INIT(head2);               \
  }                     \
} while (0)

#define LIST_EMPTY(head)  ((head)->lh_first == NULL)

#define LIST_FIRST(head)  ((head)->lh_first)

#define LIST_FOREACH(var, head, field)          \
  for ((var) = LIST_FIRST((head));        \
      (var);              \
      (var) = LIST_NEXT((var), field))

#define LIST_FOREACH_FROM(var, head, field)       \
  for ((var) = ((var) ? (var) : LIST_FIRST((head)));    \
      (var);              \
      (var) = LIST_NEXT((var), field))

#define LIST_FOREACH_SAFE(var, head, field, tvar)     \
  for ((var) = LIST_FIRST((head));        \
      (var) && ((tvar) = LIST_NEXT((var), field), 1);   \
      (var) = (tvar))

#define LIST_FOREACH_FROM_SAFE(var, head, field, tvar)      \
  for ((var) = ((var) ? (var) : LIST_FIRST((head)));    \
      (var) && ((tvar) = LIST_NEXT((var), field), 1);   \
      (var) = (tvar))

#define LIST_INIT(head) do {            \
  LIST_FIRST((head)) = NULL;          \
} while (0)

#define LIST_INSERT_AFTER(listelm, elm, field) do {     \
  QMD_LIST_CHECK_NEXT(listelm, field);        \
  if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\
    LIST_NEXT((listelm), field)->field.le_prev =    \
        &LIST_NEXT((elm), field);       \
  LIST_NEXT((listelm), field) = (elm);        \
  (elm)->field.le_prev = &LIST_NEXT((listelm), field);    \
} while (0)

#define LIST_INSERT_BEFORE(listelm, elm, field) do {      \
  QMD_LIST_CHECK_PREV(listelm, field);        \
  (elm)->field.le_prev = (listelm)->field.le_prev;    \
  LIST_NEXT((elm), field) = (listelm);        \
  *(listelm)->field.le_prev = (elm);        \
  (listelm)->field.le_prev = &LIST_NEXT((elm), field);    \
} while (0)

#define LIST_INSERT_HEAD(head, elm, field) do {       \
  QMD_LIST_CHECK_HEAD((head), field);       \
  if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL) \
    LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
  LIST_FIRST((head)) = (elm);         \
  (elm)->field.le_prev = &LIST_FIRST((head));     \
} while (0)

#define LIST_NEXT(elm, field) ((elm)->field.le_next)

#define LIST_PREV(elm, head, type, field)     \
  ((elm)->field.le_prev == &LIST_FIRST((head)) ? NULL : \
      __containerof((elm)->field.le_prev,     \
      QUEUE_TYPEOF(type), field.le_next))

#define LIST_REMOVE(elm, field) do {          \
  QMD_SAVELINK(oldnext, (elm)->field.le_next);      \
  QMD_SAVELINK(oldprev, (elm)->field.le_prev);      \
  QMD_LIST_CHECK_NEXT(elm, field);        \
  QMD_LIST_CHECK_PREV(elm, field);        \
  if (LIST_NEXT((elm), field) != NULL)        \
    LIST_NEXT((elm), field)->field.le_prev =    \
        (elm)->field.le_prev;       \
  *(elm)->field.le_prev = LIST_NEXT((elm), field);    \
  TRASHIT(*oldnext);            \
  TRASHIT(*oldprev);            \
} while (0)

#define LIST_SWAP(head1, head2, type, field) do {     \
  QUEUE_TYPEOF(type) *swap_tmp = LIST_FIRST(head1);   \
  LIST_FIRST((head1)) = LIST_FIRST((head2));      \
  LIST_FIRST((head2)) = swap_tmp;         \
  if ((swap_tmp = LIST_FIRST((head1))) != NULL)     \
    swap_tmp->field.le_prev = &LIST_FIRST((head1));   \
  if ((swap_tmp = LIST_FIRST((head2))) != NULL)     \
    swap_tmp->field.le_prev = &LIST_FIRST((head2));   \
} while (0)

#define LIST_END(head)  NULL

/*
 * Tail queue declarations.
 */
#define TAILQ_HEAD(name, type)            \
struct name {               \
  struct type *tqh_first; /* first element */     \
  struct type **tqh_last; /* addr of last next element */   \
  TRACEBUF              \
}

#define TAILQ_CLASS_HEAD(name, type)          \
struct name {               \
  class type *tqh_first;  /* first element */     \
  class type **tqh_last;  /* addr of last next element */   \
  TRACEBUF              \
}

#define TAILQ_HEAD_INITIALIZER(head)          \
  { NULL, &(head).tqh_first, TRACEBUF_INITIALIZER }

#define TAILQ_ENTRY(type)           \
struct {                \
  struct type *tqe_next;  /* next element */      \
  struct type **tqe_prev; /* address of previous next element */  \
  TRACEBUF              \
}

#define TAILQ_CLASS_ENTRY(type)           \
struct {                \
  class type *tqe_next; /* next element */      \
  class type **tqe_prev;  /* address of previous next element */  \
  TRACEBUF              \
}

/*
 * Tail queue functions.
 */
#if (defined(_KERNEL) && defined(INVARIANTS))
/*
 * QMD_TAILQ_CHECK_HEAD(TAILQ_HEAD *head, TAILQ_ENTRY NAME)
 *
 * If the tailq is non-empty, validates that the first element of the tailq
 * points back at 'head.'
 */
#define QMD_TAILQ_CHECK_HEAD(head, field) do {        \
  if (!TAILQ_EMPTY(head) &&         \
      TAILQ_FIRST((head))->field.tqe_prev !=      \
       &TAILQ_FIRST((head)))          \
    panic("Bad tailq head %p first->prev != head", (head)); \
} while (0)

/*
 * QMD_TAILQ_CHECK_TAIL(TAILQ_HEAD *head, TAILQ_ENTRY NAME)
 *
 * Validates that the tail of the tailq is a pointer to pointer to NULL.
 */
#define QMD_TAILQ_CHECK_TAIL(head, field) do {        \
  if (*(head)->tqh_last != NULL)          \
        panic("Bad tailq NEXT(%p->tqh_last) != NULL", (head));  \
} while (0)

/*
 * QMD_TAILQ_CHECK_NEXT(TYPE *elm, TAILQ_ENTRY NAME)
 *
 * If an element follows 'elm' in the tailq, validates that the next element
 * points back at 'elm.'
 */
#define QMD_TAILQ_CHECK_NEXT(elm, field) do {       \
  if (TAILQ_NEXT((elm), field) != NULL &&       \
      TAILQ_NEXT((elm), field)->field.tqe_prev !=     \
       &((elm)->field.tqe_next))          \
    panic("Bad link elm %p next->prev != elm", (elm));  \
} while (0)

/*
 * QMD_TAILQ_CHECK_PREV(TYPE *elm, TAILQ_ENTRY NAME)
 *
 * Validates that the previous element (or head of the tailq) points to 'elm.'
 */
#define QMD_TAILQ_CHECK_PREV(elm, field) do {       \
  if (*(elm)->field.tqe_prev != (elm))        \
    panic("Bad link elm %p prev->next != elm", (elm));  \
} while (0)
#else
#define QMD_TAILQ_CHECK_HEAD(head, field)
#define QMD_TAILQ_CHECK_TAIL(head, headname)
#define QMD_TAILQ_CHECK_NEXT(elm, field)
#define QMD_TAILQ_CHECK_PREV(elm, field)
#endif /* (_KERNEL && INVARIANTS) */

#define TAILQ_CONCAT(head1, head2, field) do {        \
  if (!TAILQ_EMPTY(head2)) {          \
    *(head1)->tqh_last = (head2)->tqh_first;    \
    (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last; \
    (head1)->tqh_last = (head2)->tqh_last;      \
    TAILQ_INIT((head2));          \
    QMD_TRACE_HEAD(head1);          \
    QMD_TRACE_HEAD(head2);          \
  }               \
} while (0)

#define TAILQ_EMPTY(head) ((head)->tqh_first == NULL)

#define TAILQ_FIRST(head) ((head)->tqh_first)

#define TAILQ_FOREACH(var, head, field)         \
  for ((var) = TAILQ_FIRST((head));       \
      (var);              \
      (var) = TAILQ_NEXT((var), field))

#define TAILQ_FOREACH_FROM(var, head, field)        \
  for ((var) = ((var) ? (var) : TAILQ_FIRST((head)));   \
      (var);              \
      (var) = TAILQ_NEXT((var), field))

#define TAILQ_FOREACH_SAFE(var, head, field, tvar)      \
  for ((var) = TAILQ_FIRST((head));       \
      (var) && ((tvar) = TAILQ_NEXT((var), field), 1);    \
      (var) = (tvar))

#define TAILQ_FOREACH_FROM_SAFE(var, head, field, tvar)     \
  for ((var) = ((var) ? (var) : TAILQ_FIRST((head)));   \
      (var) && ((tvar) = TAILQ_NEXT((var), field), 1);    \
      (var) = (tvar))

#define TAILQ_FOREACH_REVERSE(var, head, headname, field)   \
  for ((var) = TAILQ_LAST((head), headname);      \
      (var);              \
      (var) = TAILQ_PREV((var), headname, field))

#define TAILQ_FOREACH_REVERSE_FROM(var, head, headname, field)    \
  for ((var) = ((var) ? (var) : TAILQ_LAST((head), headname));  \
      (var);              \
      (var) = TAILQ_PREV((var), headname, field))

#define TAILQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar)  \
  for ((var) = TAILQ_LAST((head), headname);      \
      (var) && ((tvar) = TAILQ_PREV((var), headname, field), 1);  \
      (var) = (tvar))

#define TAILQ_FOREACH_REVERSE_FROM_SAFE(var, head, headname, field, tvar) \
  for ((var) = ((var) ? (var) : TAILQ_LAST((head), headname));  \
      (var) && ((tvar) = TAILQ_PREV((var), headname, field), 1);  \
      (var) = (tvar))

#define TAILQ_INIT(head) do {           \
  TAILQ_FIRST((head)) = NULL;         \
  (head)->tqh_last = &TAILQ_FIRST((head));      \
  QMD_TRACE_HEAD(head);           \
} while (0)

#define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {    \
  QMD_TAILQ_CHECK_NEXT(listelm, field);       \
  if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
    TAILQ_NEXT((elm), field)->field.tqe_prev =    \
        &TAILQ_NEXT((elm), field);        \
  else {                \
    (head)->tqh_last = &TAILQ_NEXT((elm), field);   \
    QMD_TRACE_HEAD(head);         \
  }               \
  TAILQ_NEXT((listelm), field) = (elm);       \
  (elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);    \
  QMD_TRACE_ELEM(&(elm)->field);          \
  QMD_TRACE_ELEM(&(listelm)->field);        \
} while (0)

#define TAILQ_INSERT_BEFORE(listelm, elm, field) do {     \
  QMD_TAILQ_CHECK_PREV(listelm, field);       \
  (elm)->field.tqe_prev = (listelm)->field.tqe_prev;    \
  TAILQ_NEXT((elm), field) = (listelm);       \
  *(listelm)->field.tqe_prev = (elm);       \
  (listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);    \
  QMD_TRACE_ELEM(&(elm)->field);          \
  QMD_TRACE_ELEM(&(listelm)->field);        \
} while (0)

#define TAILQ_INSERT_HEAD(head, elm, field) do {      \
  QMD_TAILQ_CHECK_HEAD(head, field);        \
  if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL) \
    TAILQ_FIRST((head))->field.tqe_prev =     \
        &TAILQ_NEXT((elm), field);        \
  else                \
    (head)->tqh_last = &TAILQ_NEXT((elm), field);   \
  TAILQ_FIRST((head)) = (elm);          \
  (elm)->field.tqe_prev = &TAILQ_FIRST((head));     \
  QMD_TRACE_HEAD(head);           \
  QMD_TRACE_ELEM(&(elm)->field);          \
} while (0)

#define TAILQ_INSERT_TAIL(head, elm, field) do {      \
  QMD_TAILQ_CHECK_TAIL(head, field);        \
  TAILQ_NEXT((elm), field) = NULL;        \
  (elm)->field.tqe_prev = (head)->tqh_last;     \
  *(head)->tqh_last = (elm);          \
  (head)->tqh_last = &TAILQ_NEXT((elm), field);     \
  QMD_TRACE_HEAD(head);           \
  QMD_TRACE_ELEM(&(elm)->field);          \
} while (0)

#define TAILQ_LAST(head, headname)          \
  (*(((struct headname *)((head)->tqh_last))->tqh_last))

/*
 * The FAST function is fast in that it causes no data access other
 * then the access to the head. The standard LAST function above
 * will cause a data access of both the element you want and
 * the previous element. FAST is very useful for instances when
 * you may want to prefetch the last data element.
 */
#define TAILQ_LAST_FAST(head, type, field)      \
    (TAILQ_EMPTY(head) ? NULL : __containerof((head)->tqh_last, QUEUE_TYPEOF(type), field.tqe_next))

#define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)

#define TAILQ_PREV(elm, headname, field)        \
  (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))

#define TAILQ_PREV_FAST(elm, head, type, field)       \
    ((elm)->field.tqe_prev == &(head)->tqh_first ? NULL :   \
     __containerof((elm)->field.tqe_prev, QUEUE_TYPEOF(type), field.tqe_next))

#define TAILQ_REMOVE(head, elm, field) do {       \
  QMD_SAVELINK(oldnext, (elm)->field.tqe_next);     \
  QMD_SAVELINK(oldprev, (elm)->field.tqe_prev);     \
  QMD_TAILQ_CHECK_NEXT(elm, field);       \
  QMD_TAILQ_CHECK_PREV(elm, field);       \
  if ((TAILQ_NEXT((elm), field)) != NULL)       \
    TAILQ_NEXT((elm), field)->field.tqe_prev =    \
        (elm)->field.tqe_prev;        \
  else {                \
    (head)->tqh_last = (elm)->field.tqe_prev;   \
    QMD_TRACE_HEAD(head);         \
  }               \
  *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);    \
  TRASHIT(*oldnext);            \
  TRASHIT(*oldprev);            \
  QMD_TRACE_ELEM(&(elm)->field);          \
} while (0)

#define TAILQ_SWAP(head1, head2, type, field) do {      \
  QUEUE_TYPEOF(type) *swap_first = (head1)->tqh_first;    \
  QUEUE_TYPEOF(type) **swap_last = (head1)->tqh_last;   \
  (head1)->tqh_first = (head2)->tqh_first;      \
  (head1)->tqh_last = (head2)->tqh_last;        \
  (head2)->tqh_first = swap_first;        \
  (head2)->tqh_last = swap_last;          \
  if ((swap_first = (head1)->tqh_first) != NULL)      \
    swap_first->field.tqe_prev = &(head1)->tqh_first; \
  else                \
    (head1)->tqh_last = &(head1)->tqh_first;    \
  if ((swap_first = (head2)->tqh_first) != NULL)      \
    swap_first->field.tqe_prev = &(head2)->tqh_first; \
  else                \
    (head2)->tqh_last = &(head2)->tqh_first;    \
} while (0)

#define TAILQ_END(head)   NULL

#endif /* !_SYS_QUEUE_H_ */
